Acinar ventilation heterogeneity in COPD relates to diffusion capacity, resistance and reactance.

The aim of this study was to investigate heterogenic ventilation in the acinar (Sacin) and conductive (Scond) airways of patients with varying chronic obstructive pulmonary disease (COPD) severity and how these relates to advanced lung function parameters, primarily measured by impulse oscillometry (IOS). A secondary aim was to investigate the effects of a short acting beta2-agonist and a muscarinic antagonist on the heterogenic ventilation. Eleven never smoking controls, 12 smoking controls, and 57 COPD patients (7 GOLD 1, 25 GOLD 2, 14 GOLD 3 and 11 GOLD 4) performed flow-volume spirometry, IOS, body plethysmography, single breath carbon monoxide diffusion, and N2-multiple breath washout. Six smoking controls and 13 of the COPD patients also performed double reversibility test by using salbutamol and its combination with ipratropium. Sacin was significantly higher in GOLD 2-4 compared to never smoking controls and smoking controls, but showed similar levels in GOLD 3 and 4. A factor analysis identified 4 components consisting of; 1) IOS parameters, 2) volume parameters, 3) diffusion parameters, Sacin and some IOS parameters and 4) Scond with central obstruction/air trapping. Salbutamol and its combination with ipratropium had no effect on Sacin and Scond. Increased Sacin in COPD was strongly related to diffusion capacity and lung volumes, but also weakly to resistance and reactance, showing a link between ventilation heterogeneity in the acinar airways and parameters measured by IOS.